Background. Lymphopenia monitoring during treatment with disease modifying drugs for MS is relevant because of the potential increased risk of infections. Lymphopenia is an anticipated effect of cladribine (CLD) treatment, given its mechanism of action.
Objectives. We aimed to i) characterize the absolute lymphocyte count (ALC) changes, and ii) evaluate the risk of infections in CLD-treated RRMS patients. ALCs were graded according to the Common Terminology Criteria for Adverse Events (CTCAE v5.0).
Materials and methods. In this observational multicentre study, demographic, clinical and MRI data of the patients included in the Free Of Charge CLD program were collected. ALC was also collected at baseline (before therapy initiation) and at month 3, 7, 12, 15, 19 and 24.
Results. 236 patients were enrolled in 56 Italian MS Centres (71% F; mean age: 39+11.5 years; mean disease duration: 10+8.5 years). The median baseline EDSS was 3.0 (quartiles 1.5-3.5; range 0-6.5). 53 patients (22.5%) were treatment naïve, 107 (45.3%) switched to CLD from first line DMDs (for inefficacy), 76 (32.2%) switched to CLD after a second line therapy (33/76 for safety reason, 43/76 for inefficacy). Mean follow up was 12.2+5 months. At baseline, median ALC was 1615.0 cell/mm3 (quartiles, 1300.0-2200.0). At month 3, ALC was available in 190/236 and 101/190 had lymphopenia: 12 (6.3%) grade 3, 47 (24.7%) grade 2 and 42 (22.1%) grade 1. Among patients presenting grade 3 at month 3, only one had persistent ALC <500 cell/mm3 at month 7. At month 7, ALC was available in 180/236 and 77/180 had lymphopenia: 1 (0.6%) grade 4, 1 (0.6%) grade 3, 43 (23.9%) grade 2 and 32 (17.8%) grade 1. Up to date, 159/236 patients were re-treated. No retreatment was delayed because of grade 4 lymphopenia. No patient presented grade 4 lymphopenia at month 15, 6/89 (6.6%) experienced grade 3, 37/89 (40.7%) grade 2, 17/89 (18.7%) grade 1. At month 19, 1/38 (2.6%) presented grade 3 lymphopenia, 11/38 (29.0%) grade 2 and 9/38 (23.7%) grade 1. At month 24, 1/9 (11.1%) patient presented grade 3 and 1/9 (11.1%) presented grade 4 lymphopenia. During treatment course, 15 patients experienced infections (1 VZV, 3 HSV), none occurring in grade 3 or 4 lymphopenia.
Conclusions. In our study, the risk of grade 3 and 4 lymphopenia was lower compared to that observed in RCT. Moreover, grade 3 lymphopenia was transient in the majority of the patients. Compared to RTC, a more favourable CLD safety profile emerged in our study.